An arrangement in which, when a latch mechanism provided on a door is in an unlocked state, a lamp as electric display means is switched ON, and when it attains a locked state the lamp is switched OFF is known from Patent Document 1. Furthermore, in the arrangement disclosed by Patent Document 1, unless the latch mechanism is switched from the unlocked state to the locked state, the lamp continues to be switched ON and power is consumed, and in order to prevent power from being wasted, an arrangement in which the time elapsed after switching ON a light-emitting element as electric display means is measured by means of a timer, and the light-emitting element is switched OFF after a predetermined time has elapsed is known from Patent Document 2.